using System;
using System.Data;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;

using Microsoft.EntityFrameworkCore;

using VNLib.Hashing;
using VNLib.Utils;
using VNLib.Utils.Memory;
using VNLib.Plugins.Extensions.Data;
using VNLib.Plugins.Essentials.Accounts;
using VNLib.Plugins.Essentials.Oauth.Tokens;

namespace VNLib.Plugins.Essentials.Oauth.Applications
{
    /// <summary>
    /// A DbStore for <see cref="UserApplication"/>s for OAuth2 client applications
    /// </summary>
    public sealed partial class Applications : DbStore<UserApplication>
    {
        public const int SECRET_SIZE = 32;
        public const int CLIENT_ID_SIZE = 16;

        private readonly PasswordHashing SecretHashing;
        private readonly DbContextOptions ConextOptions;
        private readonly ITokenManager TokenStore;

        /// <summary>
        /// Initializes a new <see cref="Applications"/> data store
        /// uisng the specified EFCore <see cref="DbContextOptions"/> object.
        /// </summary>
        /// <param name="conextOptions">EFCore context options for connecting to a remote data-store</param>
        /// <param name="secretHashing">A <see cref="PasswordHashing"/> structure for hashing client secrets</param>
        public Applications(DbContextOptions conextOptions, PasswordHashing secretHashing)
        {
            this.ConextOptions = conextOptions;
            this.SecretHashing = secretHashing;
            this.TokenStore = new TokenStore(conextOptions);
        }
      
       
        /// <summary>
        /// Updates the secret of an application, and if successful returns the new raw secret data
        /// </summary>
        /// <param name="userId">The user-id of that owns the application</param>
        /// <param name="appId">The id of the application to update</param>
        /// <returns>A task that resolves to the raw secret that was used to generate the hash, or null if the operation failed</returns>
        public async Task<PrivateString?> UpdateSecretAsync(string userId, string appId)
        {
            /*
             * Delete open apps first, incase there are any issues, worse case
             * the user's will have to re-authenticate.
             * 
             * If we delete tokens after update, the user wont see the new 
             * secret and may lose access to the updated app, not a big deal
             * but avoidable.
             */
            await TokenStore.RevokeTokensForAppAsync(appId, CancellationToken.None);
            //Generate the new secret
            PrivateString secret = GenerateSecret();
            //Hash the secret
            using PrivateString secretHash = SecretHashing.Hash(secret);
            //Open new db context
            await using UserAppContext Database = new(ConextOptions);
            //Open transaction
            await Database.OpenTransactionAsync();
            //Get the app to update the secret on 
            UserApplication? app = await (from ap in Database.OAuthApps 
                                         where ap.UserId == userId && ap.Id == appId 
                                         select ap)
                                         .SingleOrDefaultAsync();
            if (app == null)
            {
                return null;
            }
            //Store the new secret hash
            app.SecretHash = (string)secretHash;
            //Save changes
            if (await Database.SaveChangesAsync() <= 0)
            {
                return null;
            }
            //Commit transaction
            await Database.CommitTransactionAsync();
            //return the raw secret
            return secret;
        }

        /// <summary>
        /// Attempts to retreive an application by the specified client id and compares the raw secret against the 
        /// stored secret hash.
        /// </summary>
        /// <param name="clientId">The clientid of the application to search</param>
        /// <param name="secret">The secret to compare against</param>
        /// <returns>True if the application was found and the secret matches the stored secret, false if the appliation was not found or the secret does not match</returns>
        public async Task<UserApplication?> VerifyAppAsync(string clientId, PrivateString secret)
        {
            UserApplication? app;
            //Open new db context
            await using (UserAppContext Database = new(ConextOptions))
            {
                //Open transaction
                await Database.OpenTransactionAsync();
                //Get the application with its secret
                app = await (from userApp in Database.OAuthApps
                             where userApp.ClientId == clientId
                             select userApp)
                             .FirstOrDefaultAsync();
                //commit the transaction
                await Database.CommitTransactionAsync();
            }
            //make sure app exists
            if (string.IsNullOrWhiteSpace(app?.UserId) || !app.ClientId!.Equals(clientId, StringComparison.Ordinal))
            {
                //Not found or not valid
                return null;
            }
            //Convert the secret hash to a private string so it will be cleaned up
            using PrivateString secretHash = (PrivateString)app.SecretHash!;
            //Verify the secret against the hash
            if (SecretHashing.Verify(secretHash, secret))
            {
                app.SecretHash = null;
                //App was successfully verified
                return app;
            }
            //Not found or not valid
            return null;
        }
        ///<inheritdoc/>
        public override async Task<ERRNO> DeleteAsync(params string[] specifiers)
        {
            //get app id to remove tokens from
            string appId = specifiers[0];
            //Delete app from store
            ERRNO result = await base.DeleteAsync(specifiers);
            if(result)
            {
                //Delete active tokens
                await TokenStore.RevokeTokensForAppAsync(appId, CancellationToken.None);
            }
            return result;
        }      

        /// <summary>
        /// Generates a client application secret using the <see cref="RandomHash"/> library
        /// </summary>
        /// <returns>The RNG secret</returns>
        public static PrivateString GenerateSecret() => (PrivateString)RandomHash.GetRandomHex(SECRET_SIZE).ToLower()!;
        /// <summary>
        /// Creates and initializes a new <see cref="UserApplication"/> with a random clientid and 
        /// secret that must be disposed
        /// </summary>
        /// <param name="record">The new record to create</param>
        /// <returns>The result of the operation</returns>
        public override async Task<ERRNO> CreateAsync(UserApplication record)
        {
            record.RawSecret = GenerateSecret();
            //Hash the secret
            using PrivateString secretHash = SecretHashing.Hash(record.RawSecret);
            record.ClientId = GenerateClientID();
            record.SecretHash = (string)secretHash;
            //Wait for the rescord to be created before wiping the secret
            return await base.CreateAsync(record);
        }

        /// <summary>
        /// Generates a new client ID using the <see cref="RandomHash"/> library
        /// </summary>
        /// <returns>The new client ID</returns>
        public static string GenerateClientID() => RandomHash.GetRandomHex(CLIENT_ID_SIZE).ToLower();
        ///<inheritdoc/>
        public override string RecordIdBuilder => RandomHash.GetRandomHex(CLIENT_ID_SIZE).ToLower();
        ///<inheritdoc/>
        public override TransactionalDbContext NewContext() => new UserAppContext(ConextOptions);
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> AddOrUpdateQueryBuilder(TransactionalDbContext context, UserApplication record)
        {
            UserAppContext ctx = (context as UserAppContext)!;
            //get a single record by the id for the specific user
            return from userApp in ctx.OAuthApps
                   where userApp.UserId == record.UserId
                   && userApp.Id == record.Id
                   select userApp;
        }
        ///<inheritdoc/>
        protected override void OnRecordUpdate(UserApplication newRecord, UserApplication currentRecord)
        {
            currentRecord.AppDescription = newRecord.AppDescription;
            currentRecord.AppName = newRecord.AppName;
        }
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> GetCollectionQueryBuilder(TransactionalDbContext context, string userId)
        {
            UserAppContext ctx = (context as UserAppContext)!;
            //Get the user's applications based on their userid
            return from userApp in ctx.OAuthApps
                   where userApp.UserId == userId
                   orderby userApp.Created ascending
                   select new UserApplication
                   {
                       AppDescription = userApp.AppDescription,
                       Id = userApp.Id,
                       AppName = userApp.AppName,
                       ClientId = userApp.ClientId,
                       Created = userApp.Created,
                       Permissions = userApp.Permissions
                   };
        }
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> GetCollectionQueryBuilder(TransactionalDbContext context, params string[] args)
        {
            return GetCollectionQueryBuilder(context, args[0]);
        }
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> GetSingleQueryBuilder(TransactionalDbContext context, params string[] constraints)
        {
            string appId = constraints[0];
            string userId = constraints[1];
            UserAppContext ctx = (context as UserAppContext)!;
            //Query to get a new single application with limit results output
            return from userApp in ctx.OAuthApps
                   where userApp.UserId == userId
                   && userApp.Id == appId
                   select new UserApplication
                   {
                       AppDescription = userApp.AppDescription,
                       Id = userApp.Id,
                       AppName = userApp.AppName,
                       ClientId = userApp.ClientId,
                       Created = userApp.Created,
                       Permissions = userApp.Permissions,
                       Version = userApp.Version
                   };
        }
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> GetSingleQueryBuilder(TransactionalDbContext context, UserApplication record)
        {
            //Use the query for single record with the other record's userid and record id
            return GetSingleQueryBuilder(context, record.Id, record.UserId);
        }
        ///<inheritdoc/>
        protected override IQueryable<UserApplication> UpdateQueryBuilder(TransactionalDbContext context, UserApplication record)
        {
            UserAppContext ctx = (context as UserAppContext)!;
            return from userApp in ctx.OAuthApps
                   where userApp.UserId == record.UserId && userApp.Id == record.Id
                   select userApp;
        }

        //DO NOT ALLOW PAGINATION YET
        public override Task<int> GetPageAsync(ICollection<UserApplication> collection, int page, int limit)
        {
            throw new NotSupportedException();
        }
    }
}